CALCIUM-CARBONATE CEMENTATION OF SAND - A METHOD FOR PRODUCING ARTIFICIALLY CEMENTED SAMPLES FOR GEOTECHNICAL TESTING AND A COMPARISON WITHNATURAL CEMENTATION PROCESSES

The experience of Dutch dredging companies is that cemented layers in Holocene calcareous sands are much more frequent than expected. In an effort to alleviate this problem a method for producing slightly calci um carbonate cemented sand is presented, these samples being used to b etter constrain the geotechnical parameters of slightly cemented carbo nate sands when assessing dredging conditions. The most important envi ronments where early marine cementation (mainly by high-magnesian calc ite and aragonite) occur, are intertidal beaches and tidal flats, subt idal sandflats and reefs. Each environment has its typical occurrence and dimension of cemented layers and a characteristic form and distrib ution of cementing materials within the sandstone. It is, therefore, e xpected that sandstones from each environment will have a distinct set of geotechnical properties. Important factors controlling calcium car bonate cementation are the chemistry of the seawater (the source of th e cementing material) the physical conditions, in terms of hydraulic e nergy, sedimentary parameters such as permeability, texture and compos ition of the sand, and an initially stabilizer of the loose sediment. All these factors and the way in which they relate to each other expla in large variability in marine cement forms and the variability of the geotechnical properties of the cemented calcareous sediments. The fac tors controlling early cementation in the shallow-marine environment a re discussed in order to evaluate the boundary conditions for a labora tory model used to produce artificially cemented and by simulating nat ural subtidal cementation processes. The resulting cemented sands are shown to be comparable with natural sandstones and to exhibit similar behaviour during strain tests. For the purposes of assessing dredging conditions these artificial samples have advantages over natural sampl es.